JP7143553B2 - laser device - Google Patents

Description

The present disclosure relates to a laser device that emits signal light into space.

2. Description of the Related Art Conventionally, there is known a laser device that uses a coherent beam combining (CBC) technique to emit signal light, which is a high-power laser light, into space (see, for example, Patent Document 1). CBC technology is a technology that splits a single laser beam into multiple laser beams, amplifies the laser beams, and then coherently combines them.

JP-A-2000-323774

On the other hand, in a conventional laser apparatus, when transmitting signal light to a distant communication station or target, a telescope optical system is required to focus the signal light to a distant point.

As this telescope optical system, there is a Cassegrain reflective optical system that is resistant to environmental changes such as vibrations. The Cassegrain reflective optical system has a secondary mirror that expands the beam diameter of an incident laser beam, and a primary mirror that emits the expanded laser beam into space.

However, when a conventional laser device is used in combination with a Cassegrain reflective optical system, an annular mirror is used to remove the central portion of the laser beam for the purpose of avoiding heat generation due to high-power return light from the secondary mirror. After that, it is necessary to make it incident on the secondary mirror. Therefore, when the conventional laser device is used in combination with the Cassegrain reflecting optical system, the utilization efficiency of the laser light is lowered by the amount of removal of the central portion of the laser light.

The present disclosure has been made to solve the problems described above, and provides a laser device capable of improving the utilization efficiency of laser light compared to the conventional configuration even when used in combination with a Cassegrain reflective optical system. It is intended to

The laser device according to the present disclosure includes a sub-array forming unit that sub-arrays a plurality of signal lights obtained from a single laser light, and local light obtained from the laser light, and the light is arranged at a position other than the center of the optical axis. and the signal light after being sub-arrayed by the sub-arraying unit and the local light after conversion by the spatial distributing unit are combined to generate interference signal light, and the interference signal light is sent to the space. and a multiplexing unit for outputting to.

According to the present disclosure, since it is configured as described above, even when used in combination with the Cassegrain reflective optical system, it is possible to improve the utilization efficiency of laser light compared to the conventional configuration.

1 is a diagram showing a configuration example of a laser device according to Embodiment 1; FIG. 2 is a diagram showing a configuration example of an element circuit according to Embodiment 1; FIG. 2 is a diagram showing a configuration example of a collimator array according to Embodiment 1; FIG. 4 is an image diagram showing a beam arrangement example of signal light and interference signal light by local light used in the laser device according to Embodiment 1. FIG. FIG. 10 is a diagram showing a configuration example of a laser device according to Embodiment 2; FIG. 10 is an image diagram showing an example of beam arrangement of signal light and interference signal light by local light used in the laser device according to the second embodiment; FIG. 10 is a diagram showing a configuration example of a laser device according to Embodiment 3; FIG. 11 is a diagram showing an example of driving a conical prism in Embodiment 3;

Hereinafter, embodiments will be described in detail with reference to the drawings.
Embodiment 1.
FIG. 1 is a diagram showing a configuration example of a laser device according to Embodiment 1. FIG.
As shown in FIG. 1, the laser device includes a reference light source 1, a light splitter 2, a collimator lens 3, a _K circuit array 4k, a signal processor 5, a control signal generator 6, a spatial splitter 7, an inductive coupling It comprises a section 8 and Cassegrain reflective optics 9 . Here, k=1 to K, and K=2 in the first embodiment.

A reference light source 1 outputs laser light of a single frequency. As the reference light source 1, for example, a narrow linewidth laser light source that oscillates in a single mode can be used.

The optical splitter 2 splits the laser light output from the reference light source 1 into a single local light and K×N signal lights. N is a natural number of 2 or more.

The reference light source 1 and the optical distributor 2 are connected via an optical path such as an optical fiber.

The collimator lens 3 is an optical lens that collimates the local light obtained by the light distributor 2 .

The circuit array 4 _k is an optical phased array that applies variable phase modulation (variable phase control) to each of the N signal lights out of the signal lights obtained by the optical distributor 2 . The circuit array 4 _k is composed of N element circuits 41 _kn arranged in parallel, as shown in FIG. Here, n=1 to N.

The element circuit 41 _kn includes, as shown in FIG. 2, an optical phase modulator (optical phase controller) 411 _kn , an optical amplifier 412 _kn , an optical circulator 413 _kn , a photoelectric converter (photodetector) 414 _kn and a phase synchronization circuit. 415 _kn . 2, the phase synchronization circuit 415 _kn has a reference signal source 416 _kn , a variable phase shifter 417 _kn , a phase comparator 418 _kn , a loop filter 419 _kn and a signal generator 420 _kn . .

The optical phase modulator 411 _kn is a variable phase controller that modulates the phase of the signal light obtained by the optical distributor 2 . The modulation amount in the optical phase modulator 411 _kn is the modulation amount according to the optical phase control signal generated by the signal generator 420 _kn of the phase synchronization circuit 415 _kn . As the optical phase modulators 411 _kn , for example, LN (LiNbO ₃ ) phase modulators or semiconductor optical modulators can be used.

The optical amplifier 412 _kn amplifies the signal light after phase modulation by the optical phase modulator 411 _kn .

The optical circulator 413 _kn outputs the signal light amplified by the optical amplifier 412 _kn to the in-coupling section 8 . Also, the optical circulator 413 _kn outputs the light reflected by the in-coupling section 8 to the photoelectric converter 414 _kn .

The photoelectric converter 414 _kn converts the light output by the optical circulator 413 _kn into an electrical signal. Photodiodes, for example, can be used as photoelectric converters 414 _kn .

The reference signal source 416 _kn outputs an electrical signal (reference signal) having a reference frequency in a high frequency band.

The variable phase shifter 417 _kn shifts the phase of the electrical signal output by the reference signal source 416 _kn . The phase shift amount in the variable phase shifter 417 _kn is the phase shift amount according to the external control signal A41 _kn generated by the control signal generator 6 .

The phase comparator 418 _kn outputs a phase error signal having a current or voltage corresponding to the phase error between the electrical signal obtained by the photoelectric converter 414 _kn and the electrical signal after the phase shift by the variable phase shifter 417 _kn . Generate.

Loop filter 419 _kn filters the phase error signal generated by phase comparator 418 _kn to generate a control voltage.

The signal generator 420 _kn generates an optical phase control signal having an oscillation frequency corresponding to the control voltage generated by the loop filter 419 _kn .

Note that the configuration of the phase synchronization circuit 415 _kn shown in FIG. 2 is an example, and is not limited to this.

In FIG. ₁ , the number of element circuits _41-1n included in the circuit array 4-1 and the number of element circuits _41-2n included in the circuit array _4-2 are the same. However, the number of element circuits 41 _kn included in each circuit array 4 _k may be different.

The optical distributor 2 and the circuit array _4k are connected via an optical path such as an optical fiber.

The signal processing unit 5 calculates the phase shift amount in the circuit array 4 _k based on the FFP (Far Field Pattern) in the laser device or the desired wavefront shape of the output light in the Cassegrain reflecting optical system 9 .

The control signal generator 6 generates an external control signal A41- _kn for the variable phase shifter 417- _kn of the circuit array 4- _k based on the calculation result by the signal processor 5. FIG.

The spatial distribution unit 7 converts the local light (collimated light) collimated by the collimator lens 3 into a shape in which the light is arranged at a position other than the center of the optical axis. The space distribution section 7 shown in FIG. 1 is composed of a conical prism 71 and a conical prism 72 .

The conical prism 71 is a prism in which one surface in the axial direction is conical and the other surface is planar. The other surface of the conical prism 71 faces the exit surface of the collimator lens 3, and refracts the local light collimated by the collimator lens 3 to spatially distribute the light.

The conical prism 72 is a prism in which one surface in the axial direction is conical and the other surface is planar. The conical prism 72 has one surface facing the one surface of the conical prism 71, and converts the local light after spatial distribution by the conical prism 71 into annular local light. Note that the conical prism 72 may be a lens such as a conical lens, a spherical lens, or an achromatic lens.

In the above description, the case where the spatial distribution unit 7 composed of the conical prisms 71 and 72 converts the local light into an annular shape is shown. However, the present invention is not limited to this, and the space distribution unit 7 may use a prism or a lens to convert the local light into an annular shape other than an annular shape, such as an angular annular shape.

The in-coupling unit 8 sub-arrays the signal light after variable phase modulation by the circuit array 4 _k into K sets of N pieces each, and multiplexes the signal light after the sub-arraying and the local light obtained by the spatial distribution unit 7 . and emit into space. The in-coupling section 8, as shown in FIG. 1, comprises a reflecting mirror 81 _k , a collimator array 82 _k , and a beam combiner 83 _k .

Reflector 81 _k reflects the local light after conversion by spatial distributor 7 . Reflector 81 _k may be a rectangular prism.

The collimator array 82 _k has N partial reflectors 821 _kn and N optical collimators 822 _kn as shown in FIG.

The partial reflector 821 _kn reflects part of the signal light after variable phase modulation by the circuit array 4 _k and allows the rest to pass through. The above reflections may be realized using partially reflecting optics or Fresnel reflections occurring at the ends of the fibers instead of the partial reflectors 821 _kn . Also, the partial reflector 821 _kn passes the local light that has passed through the beam combiner 83 _k .
Further, in the above description, the case where part of the signal light after the variable phase modulation is reflected has been shown, but the present invention is not limited to this, and part of the signal light may be refracted.

The optical collimator 822 _kn collimates the signal light that has passed through the partial reflector 821 _kn .

The beam combiner 83 _k combines the signal light collimated by the collimator array 82 _k and the local light reflected by the reflecting mirror 81 _k and emits the combined light to the Cassegrain reflecting optical system 9 side. Also, the beam combiner 83 _k passes a part of the local light reflected by the reflecting mirror 81 _k and emits it to the partial reflector 821 _kn .

These reflecting mirror 81 _k , collimator array 82 _k and beam combiner 83 _k are arranged in an annular shape, avoiding the central part of the axicon optical system 91, according to the shape of the axicon optical system 91, as shown in FIG. be done. Reference numeral 401 in FIG. 4 denotes interference signal light generated by combining signal light and local light.

The introductory coupling section 8 includes a "sub-arraying section for sub-arraying a plurality of signal lights obtained from a single laser beam" and a "signal light after sub-arraying by the sub-arraying section and after conversion by the spatial distribution section. It corresponds to a multiplexer that generates interference signal light by multiplexing local light and emits the interference signal light into space.

The Cassegrain reflecting optical system 9 expands or reduces the beam diameter of the light after being combined by the introductory coupling section 8 . As shown in FIG. 1, the Cassegrain reflecting optical system 9 comprises an axicon optical system 91 as a secondary mirror and an axicon optical system 92 as a primary mirror.

The axicon optical system 91 is configured in a substantially convex disk shape and has a reflecting surface 911 . The reflecting surface 911 expands the beam diameter (inner diameter and outer diameter) of incident light. The reflecting surface 911 protrudes in a curved shape, and is configured such that the vertex of the curved surface is positioned at the center of the axicon optical system 91 . The axicon optical system 91 is arranged so that the reflecting surface 911 faces the in-coupling section 8 .

The axicon optical system 92 is configured in a substantially concave disk shape and has a reflecting surface 921 and a hole 922 . The reflecting surface 921 emits the light expanded by the axicon optical system 91 into space. The reflecting surface 921 is recessed in a curved surface, and is configured such that the vertex of the curved surface is positioned at the center of the axicon optical system 92 . The diameter of the reflecting surface 921 is larger than the diameter of the reflecting surface 911 . The hole 922 is a through hole configured with the vertex of the reflecting surface 921 as the axis. The axicon optical system 92 is arranged such that the axis of the hole 922 is along the optical axis of the light from the introductory coupling portion 8 . The axicon optical system 92 is arranged such that the reflecting surface 921 faces the reflecting surface 911 and the axis of the reflecting surface 921 coincides with the axis of the reflecting surface 911 .

Note that FIG. 1 shows the case where the laser device includes the Cassegrain reflecting optical system 9 . However, the present invention is not limited to this, and the Cassegrain reflecting optical system 9 may be provided outside the laser device.
FIG. 1 also shows the case where the laser device includes the reference light source 1, the light distributor 2, the collimator lens 3, the _K circuit arrays 4k, the signal processor 5, and the control signal generator 6. FIG. However, not limited to this, the reference light source 1, the light distributor 2, the collimator lens 3, the _K circuit array 4k, the signal processing unit 5, and the control signal generating unit 6 may be provided outside the laser device. good.

The laser device according to the first embodiment has a spatial distribution section 7, an in-coupling section 8 and a Cassegrain reflecting optical system 9 added to the conventional configuration.
In the laser device according to the first embodiment, the spatial distribution unit 7 converts the single local light into a shape in which the light is arranged at a position other than the center of the optical axis, and the introduction coupling unit 8 converts the light into a Cassegrain A plurality of sub-arrayed signal lights are introduced from the side of the reflecting optical system 9 and coherently combined.
As a result, the laser device according to the first embodiment can arrange the beam without being blocked by the axicon optical system 92 which is the primary mirror of the Cassegrain reflecting optical system 9 .

The laser device according to the first embodiment has the following effects as compared with the conventional configuration.

First, in the conventional configuration, it is necessary to remove the central portion of the laser beam by means of an annular mirror in order to avoid the reflected return light from the secondary mirror that constitutes the axicon optical system, which lowers the utilization efficiency of the laser beam. On the other hand, in the laser device according to the first embodiment, local light that has been converted into a shape in which light is arranged at a position other than the center of the optical axis is combined with a plurality of sub-arrayed signal lights, and the Cassegrain reflection optical system 9. As a result, this laser device can generate a beam without removing the central portion of the laser beam, and can improve the utilization efficiency of the laser beam.

In addition, in the conventional configuration, when coherently combining a plurality of sub-arrayed signal lights, in order to cover the entire beam range of each signal light, the beam diameter of the local light is expanded to maintain uniform amplitude and phase. There was a need to generate local light or a larger beam splitter. In this case, in the conventional configuration, phase noise occurs due to wavefront distortion or optical alignment error as the number of subarrays increases. On the other hand, the laser device according to Embodiment 1 converts local light into a shape in which light is arranged at positions other than the center of the optical axis. As a result, this laser device can reduce the beam diameter of the local light that is combined with the signal light, so that phase noise can be suppressed and the number of subarrays can be increased.

As described above, according to the first embodiment, the laser device includes a sub-arraying unit that sub-arrays a plurality of signal lights obtained from a single laser light, local light obtained from the laser light, Interference by combining the signal light after sub-arraying by the spatial distribution unit 7 that transforms into a shape in which light is arranged at a position other than the center of the optical axis, and the local light after conversion by the spatial distribution unit 7 and a multiplexing unit that generates signal light and emits the interference signal light into space. As a result, even when the laser device according to the first embodiment is used in combination with the Cassegrain reflecting optical system 9, it is possible to ensure output scalability and improve the utilization efficiency of the output light compared to the conventional configuration.

Embodiment 2.
In the laser device according to Embodiment 1, the case where the number of sub-arrays for signal light is 2 (K=2) was shown, but the number is not limited to this. In the laser device according to the second embodiment, the number of sub-arrays (K) of the signal light is expanded to a natural number of 2 or more to improve the emission intensity of the output light.

FIG. 5 is a diagram showing a configuration example of a laser device according to the second embodiment. The configuration example of the laser device according to the second embodiment shown in FIG. 5 is the same as the configuration example of the laser device according to the first embodiment shown in FIG. 1 except that the number of sub-arrays for signal light is different.

In the laser device according to the second embodiment, circuit arrays 4 _k , reflectors 81 _k , collimator arrays 82 _k and beam combiners 83 _k are arranged for the number of signal light sub-arrays. 6, the reflecting mirror 81 _k , collimator array 82 _k and beam combiner 83 _k are arranged in an annular shape so as to avoid the central portion of the axicon optical system 91 according to the shape of the axicon optical system 91. be. Reference numeral 601 in FIG. 6 denotes interference signal light generated by combining signal light and local light.

The laser device according to the second embodiment has the following effects as compared with the conventional configuration and the laser device according to the first embodiment.

First, in the conventional configuration, signal light and local light are combined using a beam splitter, so the number of signal light subarrays that can be added is limited to two. On the other hand, in the laser device according to the second embodiment, the number of sub-arrays of signal light is two or more, and the sub-arrays can be arranged without gaps and synthesized, so that the output of the laser light can be increased. Furthermore, since this laser device can generate a beam without removing the central portion of the laser light, an optical phased array with high synthetic efficiency can be realized.

Also, in the laser device according to the second embodiment, the multiplexed light of the signal light and the local light can be arbitrarily arranged in two or more sub-arrays. Furthermore, this laser device can apply an arbitrary external control signal A41 _kn to the variable phase shifter 417 _kn of each element circuit 41 _kn . Therefore, this laser apparatus can be conventionally configured or implemented by appropriately designing the number of arrangement of the reflecting mirrors 81 _k , the collimator array 82 _k and the beam combiner 83 _k or the external control signal A41 _kn for the variable phase shifter 417 _kn . Output light with various phase distributions can be generated as compared with the laser device according to the first aspect.

Embodiment 3.
Embodiment 3 shows a configuration in which an externally controlled driving mechanism is added to the conical prism 72 of the spatial distribution unit 7, and a variable function of the beam diameter of the light emitted from the Cassegrain reflecting optical system 9 is added.
FIG. 7 is a diagram showing a configuration example of a laser device according to Embodiment 3. In FIG. The laser device according to the third embodiment shown in FIG. 7 has a signal processing section 10 and a drive control section 11 added to the laser device according to the second embodiment shown in FIG. Other configurations are the same as those of the laser device according to the second embodiment, and the same reference numerals are given and only different parts will be described.

The signal processing unit 10 calculates the driving amount of the conical prism 72 according to the desired beam diameter.

The drive control unit 11 drives the conical prism 72 in the optical axis direction with the drive amount calculated by the signal processing unit 10 .

FIG. 8 is a diagram showing an arrangement example of the conical prisms 71 and 72. As shown in FIG.
When the distance between the conical prisms 71 and 72 changes, the beam diameter of the local light changes. Therefore, the laser device according to the second embodiment can change the beam diameter of the light emitted from the Cassegrain reflecting optical system 9 by driving the conical prism 72 in the optical axis direction. In FIG. 8, reference numeral 801 indicates the driving direction of the conical prism 72, and reference numeral 802 indicates the beam diameter of local light after conversion by the spatial distribution section 7. In FIG.

7 and 8 show the case where the drive control unit 11 drives the conical prism 72. FIG. However, not limited to this, the drive control unit 11 may drive the conical prism 71 instead of the conical prism 72 , or may drive both the conical prisms 71 and 72 .

7 and 8 show the case where the space distribution section 7 is composed of a conical prism 71 and a conical prism 72. FIG. However, even when the space distribution section 7 is composed of other prisms or lenses, control by the signal processing section 10 and the drive control section 11 can be added in the same manner as described above.

Further, the signal processing unit 10 and the drive control unit 11 correspond to "an adjustment unit that changes the beam diameter of the local light after conversion by the spatial distribution unit by driving at least one of the optical elements in the axial direction". do.

The laser device according to the third embodiment has a conventional configuration, and compared with the laser devices according to the first and second embodiments, the large-sized axicon optical system 91 and the axicon optical system 92 constituting the Cassegrain reflection optical system 9 are used. The beam diameter of the light emitted from the Cassegrain reflecting optical system 9 can be changed without driving.

It should be noted that it is possible to freely combine each embodiment, modify any component of each embodiment, or omit any component from each embodiment.

Even when the laser device according to the present disclosure is used in combination with a Cassegrain reflective optical system, it is possible to improve the utilization efficiency of laser light compared to the conventional configuration, and it is suitable for laser devices that emit signal light into space. Suitable for

1 reference light source, 2 optical distributor, 3 collimator lens, 4 _k -circuit array, 5 signal processing section, 6 control signal generating section, 7 spatial distribution section, 8 introduction coupling section, 9 Cassegrain reflection optical system, 10 signal processing section, 11 drive control unit, 41 _kn element circuit, 71 conical prism, 72 conical prism, 81 _k reflector, 82 _k collimator array, 83 _k beam combiner, 91 axicon optical system, 92 axicon optical system, 411 _kn optical phase modulator, 412 _kn optical amplifier, 413 _kn optical circulator, 414 _kn photoelectric converter, 415 _kn phase lock circuit, 416 _kn reference signal source, 417 _kn variable phase shifter, 418 _kn phase comparator, 419 _kn loop filter, 420 _kn signal generation 821 _kn partial reflector, 822 _kn light collimator.

Claims (6)

a sub-arraying unit that sub-arrays a plurality of signal lights obtained from a single laser beam;
a spatial distribution unit that converts the local light obtained from the laser light into a shape in which the light is arranged at a position other than the center of the optical axis;
a combining unit that generates interference signal light by combining the signal light after sub-arraying by the sub-arraying unit and the local light after conversion by the space distribution unit, and emits the interference signal light into space; laser device. an optical phase controller that performs variable phase control on a plurality of signal lights obtained from the laser light according to an optical phase control signal;
generated by partially reflecting or refracting the signal light after variable phase control by the optical phase controller, and combining local light obtained from the partially reflected or refracted signal light and the laser light a photodetector that converts the interference signal light into an electrical signal;
a phase synchronization circuit that generates the optical phase control signal based on the phase error between the electrical signal obtained by the photodetector and a reference signal;
2. The laser device according to claim 1, wherein the sub-array forming section collimates the signal light after the variable phase control by the optical phase controller, and forms the collimated signal light into a sub-array. 2. The laser device according to claim 1, wherein the space distribution section is configured using a plurality of optical elements including a prism or a lens. 2. The laser device according to claim 1, wherein the spatial distribution section uses a plurality of optical elements including a conical prism or a conical lens to convert local light obtained from the laser light into an annular shape. 5. The laser device according to claim 4, further comprising: an adjustment section that changes a beam diameter of the local light after conversion by the spatial distribution section by axially driving at least one of the optical elements. . 6. The laser apparatus according to any one of claims 1 to 5, further comprising a Cassegrain reflection optical system that expands or reduces a beam diameter of the interference signal light emitted by the combining section.

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